The invention relates to improvements in a hydraulic brake booster for a vehicular brake system, which is actuated by a brake pedal and which further includes a valve controlling both the interconnection of a storage source with a pressure alternation chamber in the booster as well as the interconnection of the pressure alternation chamber with a relief station. A brake booster of this type is associated with a hydraulic dual-circuit main cylinder having a return spring biased double piston for the sealing of the primary and of the secondary side and also includes a lockable protection device which cooperates with an electronic switching circuit that controls a valve mechanism for the monitoring of the charge in the two brake circuits.
For a better understanding of this invention, reference is now made to the Leiber U.S. Pat. Nos. 4,141,595 and 4,143,514, which are incorporated herein by reference.
In brake systems equipped with this general type of brake booster, it has been found that the presence of air bubbles or gas bubbles which accumulate in the pressure medium can seriously impair the braking effect. Due to the compressibility of the air or gas cushion, a substantially greater piston travel must be introduced to achieve an adequate braking effect. However, this is not practical, since it would require a main cylinder length (circa 5 times greater) and thus this structure was achieved to overcome the deficiences of the known devices.